I agree with carrieg - with Bargello's all strips are cut the same width to begin with. The difference in cutting sizes is after you join all the strips in sequence (like for a trip around the world). From that panel of joined strips, you will then start cutting across in different sizes and that difference is what will produce the waves in Bargello.
So, only cut 2 1/2 strips of each color at 3 1/2 inches.